1. Field of the Invention
The present invention relates generally to touch sensing devices used in portable electronic devices. More particularly, the present invention relates to an improved mutual capacitance sensing touch device.
2. Description of the Related Art
There are many factors that determine the size of compact portable electronic devices such as laptops, PDAs, media players, cell phones, etc. In most cases, the size of the portable electronic device is limited by the size of the operational components used therein. These components include for example microprocessor chips, printed circuit boards, displays, memory chips, hard drives, batteries, interconnectivity circuitry, indicators, input mechanisms and the like. As such, there is a desired to make these operational components smaller and smaller while maintaining or increasing their power and functionality to perform operations as well as decreasing their cost. The placement of these components inside the electronic device is also a factor in determining the size of the portable electronic device. For thin devices such as cell phones, PDAs and media players, stacking operational components on top of each other is limited and therefore the operational components may be placed side by side. In some cases, the operational components may even communicate through wires or flex circuits so that they may be spaced apart from one another (e.g., not stacked).
There exist today many styles of input mechanisms for performing operations in a portable electronic device. The operations generally correspond to moving objects and making selections. By way of example, the input devices may include buttons, keys, dials, wheels, mice, trackballs, touch pads, joy sticks, touch screens and the like. Touch devices such as touch buttons, touch pads and touch screens are becoming increasingly popular in portable electronic devices because of their ease and versatility of operation, their declining price as well as their space saving ability (e.g., planarity). Touch devices allow a user to make selections and move objects by simply moving their finger (or stylus) relative to a touch sensing surface. In general, the touch device recognizes a touch and in some circumstances the characteristics of the touch and a host controller of the portable electronic device interprets the touch data and thereafter performs action based on the touch data.
There are several types of technologies for implementing a touch device including for example resistive, capacitive, infrared, surface acoustic wave, electromagnetic, near field imaging, etc.
Capacitive touch sensing devices have been found to work particularly well in portable electronic devices. Generally speaking, whenever two electrically conductive members come close to one another without actually touching, their electric field interact to form capacitance. In the case of a capacitive touch device, as an object such as a finger approaches the touch sensing surface, a tiny capacitance forms between the object and the sensing points in close proximity to the object. By detecting changes in capacitance at each of the sensing points and noting the position of the sensing points, the sensing circuit can recognize multiple objects and determine the location, pressure, direction speed and acceleration of the object as it is moved across the touch surface.
Although capacitive sensing devices have been found to work particularly well in portable electronic devices, improvements to form, feel and functionality are still desired. For example, improvements that help produce a better portable electronic device.